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Corneal dystrophies: investigation and management.

ANTERIOR EYE AND OCULOPLASTICS PART 6 C-19711 O/D

Corneal dystrophies are primary (bilateral) inherited disorders which have distinct clinicopathological findings, are stationary or slowly progressive, and occur in the absence of inflammation, without any relationship to environmental or systemic factors. (1) The word dystrophy is derived from the Greek (dys=wrong, difficult; trophe = nourishment). This article discusses the common dystrophies which affect the cornea and describes the optometric approach to investigation and management.

Classification

A new international classification of the corneal dystrophies has been developed which takes into account the chromosomal loci of the various dystrophies, as well as the responsible genes and their mutations. A simplified version of this classification is shown in Table 1 and forms the basis of this article.2

Inheritance

Many corneal dystrophies have a genetic cause. The exact genetic cause has been identified in a large number of dystrophies, but it is beyond the scope of this article to discuss these in detail. The epithelial basement membrane, Reis-Buckler, Thiel-Behnke, Meesmann, Schnyder, lattice type I and II, granular type I and II, congenital hereditary corneal endothelial dystrophy type I, and posterior polymorphous forms of corneal dystrophy have autosomal dominant (AD) inheritance. Fuchs dystrophy may have AD inheritance in some cases, but in others it is sporadic. Macular corneal dystrophy and congenital hereditary corneal endothelial dystrophy type II have autosomal recessive (AR) inheritance. The most common location of abnormality is the transforming growth factor beta induced (TGFB1) gene and a variety of epithelial basement, Reis-Buckler, Thiel-Behnke, granular types I and II, and lattice type I corneal dystrophies have all been linked to this same gene. The TGFB1 gene contains instructions for encoding the TGFB protein, which aids the corneal layers to remain stuck together. However, an accumulation of protein, due to a mutated gene, causes symptoms associated with the dystrophy.

Epithelial and sub-epithelial dystrophies

Epithelial basement membrane dystrophy (EBMD)

This is also known as map-dot-fingerprint dystrophy, Cogan microcystic dystrophy and anterior basement membrane dystrophy. EBMD is more common in adults, rarely occurring in children, and doesn't followa pattern of inheritance. It appears as irregular islands of thickened, grey, hazy epithelium with scalloped, circumscribed borders. Dots appear as irregular oval nonstaining opacities, while fingerprints appear as parallel, curvilinear lines (Figure 1). Patients with this dystrophy are often not symptomatic, although 10% over the age of 30 years may be. A common association is recurrent corneal erosions, which occur with pain, lacrimation, polyplopia and blurred/reduced vision. However, such symptoms can fluctuate over time.

[FIGURE 1 OMITTED]

Meesman corneal dystrophy (MECD)

MECD, also known as juvenile hereditary epithelial dystrophy, follows an AD inheritance pattern and mainly occurs in childhood. It is a slowly progressive dystrophy which appears as multiple, tiny epithelial vesicles which extend to the limbus and are most numerous in the interpalpebral area, with clear surrounding epithelium. Corneal sensation may be reduced, although patients are usually asymptomatic. However, there may be mild reduction in vision with associated glare and photophobia, while recurrent corneal erosions may also occur on occasion.

Gelatinous drop-like corneal dystrophy (GDLD)

GDLD, also known as primary familial amyloidosis, follows an AR pattern of inheritance and has an age of onset in the first to second decade of life. It initially appears as sub-epithelial lesions which may be similar to band-shaped keratopathy, or groups of multiple nodules. Superficial vascularisation is frequently seen too. In later stages, stromal opacification, or large nodular lesions, can be seen. Symptoms which can be experienced include significant decrease in vision, photophobia, irritation, redness and tearing. It is slowly progressive and can even recur after corneal transplantation with a graft.

Bowman layer dystrophies

Reis-Bucklers corneal dystrophy (RBCD)

RBCD is also known as corneal dystrophy of Bowman layer type I and granular corneal dystrophy type 3. It follows an AD pattern of inheritance and has an onset in childhood. It appears as confluent irregular and coarse opacities with varying densities, initially separated but then coalescing. Opacities may extend to the limbus and deep into the stroma withtime (Figure 2). It can be confused with Thiel-Behnke corneal dystrophy (TBCD) (see later). It is slowly prokressive and causes a deterioration on vision and recurrent corneal erosions, the latter of which may resolve with time.

[FIGURE 2 OMITTED]

Thiel-Behnke corneal dystrophy (TBCD)

This dystrophy is also known as corneal dystrophy of Bowman layer type II and honeycomb-shaped corneal dystrophy. It follows an AD pattern on inheritance and has an onset in childhood. It appear as symmetrical sub-epithelial honeycomb opacities in the central cornea, with the peripheral cornea typically uninvolved initially but then extending to the limbus and deeper into the stroma with time (Fighre 3). As with R BCD, it is slowly progressive and causes deterioration of vision and recurrent corneal erosions, the latter of which may resolve with time.

Stromal dystrophies

Lattice corneal dystrophy (LCD)

LCD has AD inheritance and has an onset in the first decade of life. It is a progressive dystrophy which causes visual impairment by the fourth decade of life and is associated with ocular discomfort and pain. It often leads to recurrent corneal erosions and requires surgery in the fourth decade of life. It appears as thin branching refractile lines and/or sub-epithelial ovoid dots. The lines begin centrally and superficially and spread centrifugally and deeply. Recurrent corneal erosions which occur in the later stages are often accompanied with a diffuse stromal glass haze (Figure 4).

[FIGURE 3 OMITTED]

Granular dystrophy type 1 (GCD1)

Following an AD pattern of inheritance, GCD1 beg ins in childhood and a apears as white, well-defined granules. These opacities (to not extend to the limbus but may extend deep into the stroma and as far as Descemet's membrane. With time, the opacities become more confluent and hazy (Figure 5), being associated with a significant reduction m vision and recurrent corneal erosions, the latter of which frequent. Early symptoms include glare and photo phobia.

Granul ardystrophy type 2 (GCD2)

GCD2 (Figure 6), which also follows an AD pattern of inheritance, begins in the teen years to early adulthood. It is slowly progressive and initially appears as superficial tiny, whitish dots in the stroma. As tie dystrophy progresses, rings or stellate-shaped snowflake opacities appear between the superficial and mid-stroma, along with lattice lines deeper in the cornea. In later stages, the superficial opacities become translucent and flattened like breadcrumbs, and coalesce, causing a reduction in vision as the visual axis is affected. Pain may be associated with recurrent corneal erosions, which may occur.

Macular corneal dystrophy (MCD)

This is an AR corneal dystrophy that begins in childhood and causes severe visual impairment between the ages of 10 and 30 years. It causes a reduction in corneal sensitivity and photophobia, with recurrent corneal erosions. Initially, it appears as a diffuse stromal haze which extends to the limbus. In later stages, it produces superficial, central, elevated and irregular whitish opacities called macules (Figure C). Unlike granular dystrochy, there are no clear Spaces between the opacities. In the later stages, the endothelium may also be affected. People affected by this dystrophy normally have a thin cornea.

[FIGURE 4 OMITTED]

Schnyder dystfophy (SCD)

This AD corneal dystrophy can appear in childhood, but in most cases the diagnosis is only made in the second or third decade of life. Corneal changes which occur are predictable on the basis of age, with young patients having central corneal haze and/or sub-epithelial crystals, which then lead to arcus lipoides. However, only 50%of patients will have corneal crystals. In the fourth decade of life, mid-peripheral panstromal haze appears. With age, vision reduces and glare increases. Scotopic vision may be remarkably good but photopic vision is disproportionately reduced. Corneal sensation decreases with age and patients may have hyperlipoproteinemia.

Descemet's membrane and endothelial dystrophies

Fuchs endothelial dystrophy (FECD)

Most cases ere VECD are sporadic, although some follow AD inheritance. It normally has an onset in the fourth decade of life and later but this is very variable. It appears with corneal guttata, which can be seen on slit lamp examination as beaten-metal endothelial changes, with or without pigment dusting. Endothelial dysfunction then leads to stromal oedema (Figure 8). Sup-epithelial fibrous scarring can occur along with superficial vascularisation in chronic disease. Symptoms range from intermittent to permanent reduction in vision from stromal oedema, while pain, photophobia and epiphora can occur from recurrent corneal erosions, which in turn occur from burst bullae.

[FIGURE 5 OMITTED]

Posterior polymorphous dyshrophy (PPCD)

This AD dystrophy occurs in early childhood and is often asymmetric. It is not normally associated with symptoms unless there is rare stromal clouding as a result of endothelial decompensation. There are deep corneal lesions of various shapes, including nodular, vesicular or blister-like, occurring in isolation, clusters or confluent (better seen in retro-illumination) (Figure 9). The vesicles slowly progress and there is thickening of Descemet's membrane over a period of years. In about 25% of people affected, there can be peripheral iridocorneal adhesions and in 15% of people there can be raised IOP.

[FIGURE 6 OMIITED]

Congenital hereditary endothelial dystrophy(CHED)

This AD dystrophy occurs in the first or second decade of life and is occasionally present soon after birth. There is asymmetric corneal clouding ranging from a (diffuse haze to a milky, ground-glass appearance. There is associated chickening of the cornea and blurred vision, photophobia, and lacrimation. There may be corneal endothelial decompensation over a prolonged period of time. In other cases, there is exclusive peau d'orange-like endothelial alterations, with no, or little, objective reduction of vision.

Investigation

Of greatest importance for the examination of a suspected corneal dystropy is to perform a slit lamp examination, using the full range of observation and illumination techniques and levels of magnification. Indeed, in the early stages of a corneal dystrophy, only subtle changes might be observable and therefore careful examination is required. Epithelial dystrophies can be observed in direct light, while stromal dystrophies can be identified using an optic section. Endothelial opacities will retire high magnification and specular reflection. The effect on vision will also need to be evaluated, as symptomatic reductions will require management.

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

Differential diagnosis can be aided by answering the following questions:

* What age is the patient?

* Which layer(s)of the cornea involved?

* What is the pattern of involvement?

* What symptoms are present, if any?

* Doer any other family member have problems (worth examining them)

If a patient is asymptomatic, referral to the hospital eye service (HIES) can be worth while, in order to establish a diagnosis and to allow genetic counselling for the family if appropriate. Beyond this, management is based on symptomatic cases anp hence, optometrist can play a major role through support, recommendation of lubrication and bandage contact lens fitting for painful disease (including recurrent corneal erosions) and fitting of rigid gas permeable (RGP) contact lenses (before and after grafting). Where patients do not respond to any of these measures, or there is concern about the effect on visual function and lifestyle, patients should be referred to the HES for further management.

Management

Epithelial disease

The first-time treatment options usually involve the use of night-time lubricating ointments such as Lacrilube, simple eye ointment or VitA-Pos (netpust standarp artificial tears). The second line treatment is fitting of extended wear contact lenses for four to six weeks. Symptomatic acute corneal erosions may be treated with bandage contact lenses, antibiotic ointments, or patching. Topical steroids or oral Doxycycline may provide some benefit to prevent recurrence. Surgical intervention, such as anterior stromal puncture (outside the visual axis), YAG laser micropuncture, cautery, alcohol-assisted epithelial debridement, and excimer laser phototherapeutic keratectomy (PTK) can be of benefit in reducing the rate of recurrent erosions.

Stromal disease

Recurrent corneal erosions are treated as in epithelial diseases. An assessment needs to be made of the depth of the dystrophy in the cornea, eg anterior segment OCT. Superficial lesions are occasionally helped by RGP lens fitting, or removal with PTK (this will induce a hyperopic shift in refractive error). Otherwise, disease in the superficial 50% of the cornea is amenable to automated lamellar keratoplasty, with a microketatome or femtosecond laser, or deep lamellar feratoplasty if deeper than 50% of cornea is affected. It is far more preferable to perform lamellar surgery and only remove the diseased area rather than a penetrating keratoplasty to remove the entire cornea. This is because there is faster visual recovery, reduced rate of rejection of corneal tissue, reduced regular and irregular astigmatism, and reduced suture-related problems.

Endothelial disease

This is managed conservatively with hypertonic saline and lubrication initially. Wherever possible, if it is purely endothelial disease, then the best surgical procedure is a Descemet's membrane-stripping endothelial keratoplasty (sometimes augmented by a superficial keratectomy for any scarring). Only if this is not possible does one revert to a penetrating keratoplasty. Conservative measures include a bandage contact lens or amniotic membrane graft.

[FIGURE 9 OMITTED]

Module questions Course code: C-19711 O/D

PLEASE NOTE There is only one correct answer. All CET is now FREE. Enter online. Please complete online by midnight on November 2, 2012--You will be unable to submit exams after this date. Answers to the module will be published on www.optometry.co.uk/cet/exam-archive. CET points for these exams will be uploaded to Vantage on November 12,2012. Find out when CET points will be uploaded to Vantage at www.optometry.co.uk/cet/vantage-dat

1. Which of the following is TRUE about corneal dystrophies?

a. They are usually not inherited

b. They usually have autosomal dominant inheritance

c. They usually have autosomal recessive inheritance

d. They usually have sporadic inheritance

2. Which of the following is TRUE about Fuchs endothelial dystrophy?

a. It usually has autosomal dominant inheritance

b. It typically appears before the age of 30 years

c. Early treatment could prevent vascularisation and scarring

d. It always needs corneal transplantation

3. Which of the following is TRUE about stromal corneal dystrophies?

a. They are usually static

b. Symptoms can include glare and photophobia

c. All types cause recurrent erosions

d. They always have systemic sequelae

4. Which of the following is TRUE about Bowman layer dystrophies?

a. Reis-Bucklersand Thiel-Behnke are easy to differentiate clinically

b. They normally occur in late adulthood

c. They are not associated with genetic inheritance

d. Most type a are associated with significant reduction of visual acuity

5. Which of the following is TRUE about epithelial basement membrane dystrophy?

a. It is a synonym for Meesman's dystrophy

b. It is very rare, occurring in 0.1% of people

c. It is always symptomatic

d. It can cause polyplopia

6. Which of the following is TRUE about the management of corneal dystrophies?

a. They will always require corneal transplantation eventually

b They are best managed by penetrating keratoplasty

c. The surgical treatment of choice is lamellar keratoplasty

d. Management is through surgical means only

References

See www.optometry.co.uk/clinical. Click on the article title and then on 'references' to downed.

Sunil Shah, MBBS, FRCOphth, FRCS(Ed), FBCLA

Amit Patel, MB BCh, FRCOphth

Professor Sunil Shah is a consultant ophthalmologist at the Midland Eye Institute, Birmingham and Midland Eye Centre, and honorary consultant at Birmingham Children's Hospital. He is also an honorary professor at the University of Ulster and visiting professor at Aston University, Birmingham. He specialises in complex corneal and refractive surgery. Professor Shah is past president of the British Society for Refractive Surgery (BSRS) and is a specialist adviser to the National Institute for Clinical Excellence and British Standards Institute. Amit Patel is a consultant ophthalmologist at the Heart of England NHS Trust and Midland Eye Institute in Birmingham. He has a special interest in corneal, cataract and refractive surgery. He is a treasurer of the BSRS and a council member of the Medical Contact Lens and Ocular Surface Association.
Table 1

Types of corneal dystrophies

Epithelial and sub-epithelial dystrophies

Bowman layer dystrophies

Stromal dystrophies

Descemet membrane and endothelial dystrophies
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Title Annotation:CONTINUING EDUCATION & TRAINING
Author:Shah, Sunil; Patel, Amit
Publication:Optometry Today
Geographic Code:4EUUK
Date:Oct 5, 2012
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